1. Field of the Invention
The present invention relates to a technique for detecting the ejection of ink drops by a printing apparatus.
2. Description of the Related Art
In an ink-jet printer, ink drops are ejected from a plurality of nozzles to print images. The print head of an ink-jet printer is provided with a plurality of nozzles, some of which are occasionally plugged and rendered incapable of ejecting ink drops. This is caused by an increase in ink viscosity, the entry of gas bubbles, or other factors. Such inability to eject ink drops produces images with missing dots and has an adverse effect on image quality. The ejection of ink drops should therefore be monitored before or during printing.
Detection methods based on the use of light have been proposed as a means of monitoring the ejection of ink drops. Such detection methods allow the operation of each nozzle to be confirmed by moving the print head in order to dispose the nozzles at specific positions, and causing each nozzle to eject ink drops to block light from a detection device.
However, this testing operation requires that detection data be acquired and processed for each nozzle. The resulting drawback is that considerable time is required to acquire and process such detection data.
Accordingly, an object of the present invention is to detect inoperative nozzles without acquiring detection data for each nozzle.
In order to attain the above and the other objects of the present invention, there is provided a method for testing ejections of ink drops with a print head including a nozzle row having a plurality of nozzles. The testing method comprises the steps of: generating a light beam concurrently intersecting a plurality of paths of ink drops ejected from N target nozzles for the testing, N being an integer of 2 or more; providing the N target nozzles with drive signals to eject ink drops; generating detection pulses in response to blockage of the light beam by the ejected ink drops; and detecting presence or absence of inoperable nozzle incapable of ejecting ink drops by analyzing the detection pulses.
In the printing method of the present invention, the presence of the inoperative nozzle can be detected without acquiring detection data for each nozzle. Because each of the plurality of nozzles is detected and it is determined whether the each plurality of nozzles contain inoperative nozzles.
In the printing method of the present invention, the testing method further comprising the steps of updating the target nozzles by moving at least one of the print head and the light beam; and repeating the above mentioned steps until the testing is performed on all the plurality of nozzles.
In a preferred method of the present invention, the step (d) includes the step of determining presence or absence of the inoperative nozzle among the N target nozzles if a value of a detection pulse is less than a predetermined first threshold value.
This configuration can be readily adapted to a printing device because the presence or absence of inoperative nozzles among the target nozzles can be established by comparing detection pulses with a predetermined threshold value.
In a preferred embodiment of the invention, the step (b) includes the step of setting a constant frequency for the drive signals; and the step (d) includes the steps of generating a nozzle detection signal by filtering out a component of the constant frequency from the detection pulses; and determining presence or absence of the inoperative nozzle among the N target nozzles if a value of the nozzle detection signal is less than a predetermined second threshold value.
This arrangement makes it possible to establish the presence or absence of inoperative nozzles with greater accuracy because only signals generated in accordance with the ejection of ink drops can be extracted.
In a preferred embodiment of the invention, the testing method further comprises the step of cleaning a nozzle row including the detected inoperative nozzle
This arrangement makes it possible to reduce the consumption of ink during nozzle cleaning because the missing of dots (the presence of inoperative nozzles) can be prevented by cleaning only part of the plurality of nozzles provided to the print head.
In a preferred embodiment of the invention, sequentially providing each of the N target nozzles with the drive signals one by one if the inoperative nozzle is detected among the N target nozzles; generating detection pulses in response to blockage of the light beam by the ink drops ejected from each of the N target nozzles; and identifying the inoperative nozzle in response to the detection pulses.
This arrangement makes it possible to identify the inoperative nozzles among other nozzles, allowing printing to be continued by, supplementing the inoperative nozzles with other nozzles when missing dots are detected during printing, for example.
In a preferred embodiment of the invention, the step (b) includes the steps of setting N types of mutually different frequencies for the drive signals; and providing each of the N target nozzles with each of the N types of mutually different frequencies, respectively; and the step (d) includes the steps of filtering out N components of the N types of mutually different frequencies from the detection pulses generating nozzle detection signals as chronological data for each of the N components; and identifying the inoperative nozzle among the N target nozzles by comparing an order of the nozzle detection signals in the chronological data.
This arrangement makes it possible to identify inoperative nozzles without repeating detection of each tested nozzle for the presence of inoperative nozzles.
In a preferred embodiment of the invention, the N types of ejection frequencies are set such that any multiples of the N types of mutually different frequencies is different from any of the N types of mutually different frequencies.
This arrangement makes it possible to avoid situations in which the frequency of a nozzle detection signal coincides with the higher harmonic of the nozzle detection signal for a nozzle belonging to a different nozzle group. This allows inoperative nozzles to be detected with higher accuracy by suppressing higher-harmonic noise.
The present invention can be realized in various forms such as a method and apparatus for printing, a method and apparatus for producing print data for a printing unit, and a computer program product implementing the above scheme.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.